DE102021213293A1 - Method of operating switchgear and switchgear - Google Patents

Abstract

The ratio of two time constants of the temperature adjustment to a step-like current change is determined from a fit of measured values from at least two temperature sensors arranged near a first and second screw connection, and a fault in the area of one of the screw connections is inferred from the deviation of the ratio from a value of 1.

Description

The invention relates to a switchgear, in particular for medium and/or high voltages.

A common source of error in a switchgear is the screw connections in the switchgear, especially those that are assembled on site. The screw connection on the busbar and on the high-voltage cable play an important role here. These screw connections can deteriorate over the course of operation, resulting in additional local heating that can ultimately lead to a fault. Early identification of such a fault location can be used for anticipatory troubleshooting.

From the U.S. 2017/0148300 A1 It is known to compare values for the absolute temperature between the individual phases of the switchgear in order to detect a possible fault. It is assumed that such a defect occurs in only one phase.

It is also known to relate the temperature increase over the ambient temperature to the square of the current using a linear equation. The change in the linear equation is then considered for the status assessment.

A disadvantage of the known methods is that comparisons of the temperature between phases require a symmetrical current load and the influence of some errors on the absolute temperature is small, so that error detection is difficult.

It is the object of the invention to specify an improved method for determining the status of a switchgear and a correspondingly improved switchgear.

This object is achieved by a switchgear with the features of claim 1.

In the operating method according to the invention for a switchgear, signals are recorded by two temperature sensors arranged in the switchgear. Furthermore, a ratio of two thermal time constants for temperature changes at the temperature sensors is determined on the signals by a function that models a ratio of the curves of the temperatures at the temperature sensors. Finally, an alarm signal is generated when the thermal time constant ratio is within an error range.

The switching system according to the invention comprises a temperature sensor and an evaluation device, the evaluation device being designed to carry out the method. The evaluation device is therefore designed to record signals from two temperature sensors arranged in the switchgear, to determine a ratio of two thermal time constants for temperature changes at the temperature sensors to the signals using a function that models a ratio of the temperature profiles at the temperature sensors, and an alarm signal to generate when the ratio of the thermal time constants is in an error range.

The switchgear can be air-insulated switchgear (AIS) or gas-insulated switchgear (GIS).

Advantageously, the absolute values of temperatures are not compared in the present invention, but time constants are considered, with which an adjustment of the temperature takes place after a change in the thermal influences, in particular after a change in current. Since these are determined with a fit to a function, signal noise and other statistical influences are automatically minimized. Furthermore, the time constants are also visible with small changes in the thermal influences and are not dependent on the current loading of different phases being symmetrical.

What is particularly advantageous with this method is that by forming the ratio of the two time constants under consideration, two influencing factors can be neglected, namely the ambient temperature and the electrical losses of the switchgear, which lead to the temperature change. Since these are not necessarily known or available as measured values, considering the ratio of the time constants results in a simplified and improved fitting process that leads to more reliable results.

• Als Fehlerbereich können alle Werte für das Verhältnis der Zeitkonstanten verwendet werden, die weiter als ein Mindestabstand von 1 oder weiter als ein Mindestfaktor von 1 entfernt liegen. Beispielsweise kann der Fehlerbereich alle Verhältnisse umfassen, die außerhalb des Intervalls von 0,8 bis 1,2 liegen; hier beträgt also der Mindestabstand 0,2. Alternativ kann der Fehlerbereich beispielsweise alle Verhältnisse umfassen, die außerhalb des Intervalls von 0,8 bis 1,25 liegen; hier wird ein Mindestfaktor von 0,8 verwendet.

Advantageous refinements of the method according to the invention and the switchgear according to the invention are evident from the dependent claims. The embodiment of the independent claims can be combined with the features of one of the subclaims or preferably also with those of several subclaims. Accordingly, the following features can also be provided:

• Any values for the ratio of the time constants that are more than a minimum distance of 1 or more than a minimum factor of 1 away can be used as the error range. For example, the error range can include all ratios outside the interval from 0.8 to 1.2; here the minimum distance is 0.2. Alternatively, the error range may include, for example, all ratios that are outside the interval 0.8 to 1.25; a minimum factor of 0.8 is used here.

The function can describe the temperature curve under the assumption that the temperature sensors are connected to an ambient temperature via a first-order thermal network, each with a thermal mass and a thermal resistance, with the ambient temperature being disregarded in the function.

A safety measure is preferably carried out upon receipt of the alarm signal. This can involve, for example, reducing a current flowing through the switchgear, in particular through an affected phase, switching off the switchgear, or initiating a maintenance measure. For example, the urgency or the degree of the security measure can be made dependent on the extent of the deviation below the reference value.

The switchgear can comprise one phase or several phases, in particular three phases, and can furthermore comprise a temperature sensor for each phase.

The temperature sensors are preferably located in a thermally closely coupled system, for example in the cable connection room.

The temperature sensors are preferably designed to measure temperatures of screw connections. For this purpose, they are preferably arranged close to such screw connections. Since thermal time constants of thermal matching are determined, it is not necessary that the temperature sensors be located directly at the bolted joints, but it is convenient if they are located so close to them that the thermal influence of one fault on the bolted joints outweighs the influence of others Screw connections, for example those of other phases, clearly predominates.

The temperature sensors can be arranged, for example, on a busbar connection, a cable connection, an upper outlet, a lower outlet or on a bushing.

As an alternative to an evaluation, that is to say carrying out the fitting process in the switchgear itself, it is also possible for the switchgear to be coupled to a computer system which is separate from the switchgear, in particular designed as a cloud service. The switchgear is expediently designed to transmit the existing measured values, ie at least the temperature profile, to the computer system. The computer system, in turn, is designed to carry out the fitting process using at least the temperature profile. The advantage here is that the data is processed centrally and the computing and storage capacity in the computer system is typically many times higher than in a switchgear, since switchgear is usually at best equipped with a microcontroller, whereas computer systems work with microprocessors.

• 1 eine luftisolierte Schaltanlage mit einem Temperatursensor,
• 2 ein thermisches Modell für die Schaltanlage,
• 3 einen T-Stecker einer Schaltanlage mit Platzierungsmöglichkeiten für einen Temperatursensor.

The invention is described and explained in more detail below with reference to the exemplary embodiments illustrated in the figures. Show it:

• 1 an air-insulated switchgear with a temperature sensor,
• 2 a thermal model for the switchgear,
• 3 a T-plug of a switchgear with placement options for a temperature sensor.

1 shows an embodiment of a switchgear 1 in a cross-sectional view. The switchgear 1 is designed here as an air-insulated switchgear, but the invention can also be applied to gas-insulated or other switchgear of low, medium or high voltage technology.

The switchgear 1 of 1 has four different rooms, which are separated from each other by partitions. A busbar compartment 4 houses a set of busbars 14 (usually one bar per phase of the power system) over which electrical power is distributed between a plurality of adjacent switchgear. The respective busbar spaces 4 can be connected directly to one another and thus form a common busbar space or be separated from one another.

The busbars 14 arranged in the busbar space 4 are connected via connecting conductors 16 to upper outlets 12 of a switching device 10 located in a device space 2, with so-called contact tulips or finger contacts for example being able to be used to provide detachable contacts for easy replacement of the switching device 10. Circuit breakers, load switches, short-circuiters, grounding switches, fuses and the like can be used as switching device 10, for example.

Lower outlets 13 of the switching device 10 are connected in a corresponding manner via connecting conductors 16 to cables 15 located in a cable connection room 3 , which can serve as inputs or outputs for the electrical energy distributed by the switchgear 1 .

The connecting conductors 16 are electrically connected to the switching device 10 via bushings 11 between the equipment compartment 2 on the one hand and the busbar compartment 4 or the cable connection compartment 3 .

A low-voltage space 5 can accommodate control electronics, measuring and signaling devices and other such low-voltage auxiliary devices. These low-voltage auxiliary devices can read readings from the various live and live components and forward them to remote devices for control and protection purposes and/or display them locally and/or evaluate them automatically. In order to provide such measured values, current and voltage transformers are usually attached to the busbars and the cables, the measurement outputs of which are connected to the low-voltage auxiliary devices.

The connections between the upper and lower outlets 12, 13 and the switching device 10, between the upper and lower outlets 12, 13 and the bushings 11, between the bushings 11 and the connecting conductors 16 and between the connecting conductors 16 and the busbars 14 or the cables 15 can be made using non-positive connections such as screw or clamp connections. Increased heat generation can therefore occur at these points if the quality of an electrical contact produced in this way is too low.

Therefore, in this example, three temperature sensors 18a...c are arranged in the cable connection compartment 3 in the vicinity of three analogue screw connections, each of which is part of a phase. The temperature sensors 18a...c are thus very close to their respective screw connection and also close to one another—in comparison to the size of the switchgear 1. The temperature sensors 18a...c are communicatively connected to an evaluation unit 17, which is shown as part of the switchgear 1 in this case. In the present case, the evaluation unit 17 is arranged in the low-voltage space 5 and can be part of another low-voltage auxiliary device. In other embodiments, the functionality of the evaluation unit 17 can also be arranged outside of the switchgear 1, for example in a separate computer or in a cloud service. In all cases there is at least an indirect data connection between the temperature sensors 18a...c and the evaluation unit 17, through which measured values of the temperature sensors 18a...c can be transmitted to the evaluation unit 17.

The communicative connection between the temperature sensors 18a...c and the evaluation unit 17 can be implemented via an electrical or optical data line, a wireless communication link or via near-field communication. In the latter case, the temperature sensors 18a...c are excited electromagnetically via antennas (not shown) in the cable connection compartment 3 of the switchgear 1 and are read based on their reaction to the electromagnetic excitation. This offers the advantage that the temperature sensors 18a...c can be set up electrically isolated from the evaluation unit 17 and also without batteries for the supply of a wireless communication link.

If the current flowing through the switchgear 1 changes, then the power loss occurring in the switchgear also changes according to P _V =I ² *R 1 , where I is the current flowing and R is the electrical resistances present in the switchgear 1 . This changes the temperature in the switchgear 1, which is reflected in the sensor signal from the temperature sensors 18a...c. The entire switchgear 1 forms a complex thermal system in which temperature changes propagate. The fastest visible in the signal of a temperature sensor 18a...c are those temperature changes that occur close to the temperature sensor 18a...c, ie in particular temperature changes due to the screw connection in the immediate vicinity of which the temperature sensor 18a...c is arranged.

Typical time constants with which the temperature adapts after a change in current are about 1 hour. If the screw connection under consideration is faulty and causes a considerable additional heat input, this is reflected in a reduced time constant of the temperature change.

It is possible to determine the time constants by means of an evaluation, for example a fit to the measurement data. The functional connection results from a model that 2 is shown. The functional connection results from a model that 2 is shown. In this model, the superposition of many thermal time constants and power losses is simplified to a simple model structure with a single heat source connected via a first-order thermal network with an RC element consisting of a thermal mass 21 and a thermal Resistor 22 is connected to the outside temperature 23 as a heat sink. In the event of an error, the superposition is dominated by the faulty screw connection 20 .

For the first-order thermal network as in 2 shown, the following relationship results: $$T_{Amb}\left(t\right)=\tau \cdot \dot{T}\left(t\right)+T\left(t\right)-P_{LOss}\left(t\right)\cdot R$$

In this case, T _Amb is the ambient temperature 23, T is the temperature of a respective temperature sensor 18a...c, P _Loss is the power loss that occurs and R is the size of the thermal resistance 22. The parameter τ is the time constant of the temperature adjustment sought for this temperature sensor 18a... c. It can be seen that at a constant outside temperature and constant power loss, an exponential curve of the temperature T results after a stepwise change in the power loss. However, it cannot generally be assumed that these values are constant.

Furthermore, it cannot be assumed that the values for the ambient temperature are known at all. On the one hand, the switchgear can be designed in such a way that it does not have a sensor for this. On the other hand, in some embodiments of the invention, the evaluation cannot take place in the switchgear itself but, for example, in a cloud server where measured values for the ambient temperature are not available because they are not transmitted. The same applies to the electrical losses P _Loss of the switchgear.

$$T_{Amb}\left(t\right)={\tau }_2\cdot {\dot{T}}_{M2}\left(t\right)+T_{M2}\left(t\right)-P_{Loss}\left(t\right)\cdot R_2$$

A combination of the relationships for two of the temperature sensors 18a...c is therefore advantageously carried out: $$T_{Amb}\left(t\right)={\mathrm{<figure-callout\; id="1"\; label="\tau "\; filenames="DE102021213293A1\_0009.png"\; state="\{\{state\}\}">\tau </figure-callout>}}_1\cdot {\dot{T}}_{M1}\left(t\right)+T_{M1}\left(t\right)-P_{LOss}\left(t\right)\cdot {\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="DE102021213293A1\_0009.png"\; state="\{\{state\}\}">R</figure-callout>}}_1$$

$$T_{Amb}\left(t\right)={\mathrm{<figure-callout\; id="2"\; label="\tau "\; filenames="DE102021213293A1\_0009.png"\; state="\{\{state\}\}">\tau </figure-callout>}}_2\cdot {\dot{T}}_{M2}\left(t\right)+T_{M2}\left(t\right)-P_{LOss}\left(t\right)\cdot {\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="DE102021213293A1\_0009.png"\; state="\{\{state\}\}">R</figure-callout>}}_2$$

$$0=\frac{{\tau }_2\cdot {\dot{T}}_{M2}\left(t\right)}{T_{M2max}}+\frac{T_{M2}\left(t\right)}{T_{M2max}}-\left(P_{Loss}\left(t\right)+\frac{T_{Amb}\left(t\right)}{R_2}\right)\cdot \frac{R_2}{T_{M2max}}$$

The indices M1 and 1 denote the values belonging to a first temperature sensor 18a...c and the indices M2 and 2 denote the values belonging to a second temperature sensor 18a...c. After conversion and normalization to the respective maximum temperature T _M1max or T _M2max , the result is: $$0=\frac{{\mathrm{<figure-callout\; id="1"\; label="\tau "\; filenames="DE102021213293A1\_0009.png"\; state="\{\{state\}\}">\tau </figure-callout>}}_1\cdot {\dot{T}}_{M1}\left(t\right)}{T_{M1max}}+\frac{T_{M1}\left(t\right)}{T_{M1max}}-\left(P_{LOss}\left(t\right)+\frac{T_{Amb}\left(t\right)}{R_1}\right)\cdot \frac{R_1}{T_{M1max}}$$

$$0=\frac{{\mathrm{<figure-callout\; id="2"\; label="\tau "\; filenames="DE102021213293A1\_0009.png"\; state="\{\{state\}\}">\tau </figure-callout>}}_2\cdot {\dot{T}}_{M2}\left(t\right)}{T_{M2max}}+\frac{T_{M2}\left(t\right)}{T_{M2max}}-\left(P_{LOss}\left(t\right)+\frac{T_{Amb}\left(t\right)}{R_2}\right)\cdot \frac{R_2}{T_{M2max}}$$

$${\tau }_2=\frac{T_{M2max}}{T_{M1max}}\cdot \frac{{\dot{T}}_{M1}\left(t\right)}{{\dot{T}}_{M2}\left(t\right)}\cdot {\tau }_1\frac{T_{M2max}}{{\dot{T}}_{M2}\left(t\right)}\cdot \left(\frac{T_{M1}\left(t\right)}{T_{M1max}}-\frac{T_{M2}\left(t\right)}{T_{M2max}}+B\right)$$

Mit $$B=\frac{-\left(P_{Loss}\left(t\right)+\frac{T_{{}_{Amb}\left(t\right)}}{R1}\right)}{\left(P_{Loss}\left(t=t1\right)+\frac{T_{{}_{Amb}\left(t=t1\right)}}{R_1}\right)}+\frac{\left(P_{Loss}\left(t\right)+\frac{T_{{}_{Amb}\left(t\right)}}{R_2}\right)}{\left(P_{Loss}\left(t=t2\right)+\frac{T_{{}_{Amb}\left(t=t2\right)}}{R_2}\right)}$$

Further rearrangement results in an expression for the relation of the two time constants τ ₁ and τ ₂ : $${\mathrm{<figure-callout\; id="2"\; label="\tau "\; filenames="DE102021213293A1\_0009.png"\; state="\{\{state\}\}">\tau </figure-callout>}}_2=\frac{T_{M2max}}{{\dot{T}}_{M2}\left(t\right)}\cdot \left(\frac{{\tau }_1{\dot{T}}_{M1}\left(t\right)}{T_{M1max}}+\frac{T_{M1}\left(t\right)}{T_{M1max}}-\frac{T_{M2}\left(t\right)}{T_{M2max}}+B\right)$$

$${\mathrm{<figure-callout\; id="2"\; label="\tau "\; filenames="DE102021213293A1\_0009.png"\; state="\{\{state\}\}">\tau </figure-callout>}}_2=\frac{T_{M2max}}{T_{M1max}}\cdot \frac{{\dot{T}}_{M1}\left(t\right)}{{\dot{T}}_{M2}\left(t\right)}\cdot {\tau }_1\frac{T_{M2max}}{{\dot{T}}_{M2}\left(t\right)}\cdot \left(\frac{T_{M1}\left(t\right)}{T_{M1max}}-\frac{T_{M2}\left(t\right)}{T_{M2max}}+B\right)$$

With $$B=\frac{-\left(P_{LOss}\left(t\right)+\frac{T_{{}_{Amb}\left(t\right)}}{R1}\right)}{\left(P_{LOss}\left(t=t1\right)+\frac{T_{{}_{Amb}\left(t=t1\right)}}{R_1}\right)}+\frac{\left(P_{LOss}\left(t\right)+\frac{T_{{}_{Amb}\left(t\right)}}{R_2}\right)}{\left(P_{LOss}\left(t=t2\right)+\frac{T_{{}_{Amb}\left(t=t2\right)}}{R_2}\right)}$$

By normalizing and considering the two time constants or the gradients relative to one another, term B can be neglected and still achieve sufficient accuracy to identify faults. This means that no additional current measurement or measurement of the ambient temperature is necessary, which is a special feature of this method. Since the parameters τ ₁ and τ ₂ are unknown, a fitting procedure is used. In this case, a separate value for the parameters τ ₁ and τ ₂ is not determined in each case, but only the relation τ ₁ /τ ₂ . The relation is a sufficient indicator for a comparative determination of the status. The relation could also be determined if τ ₁ and τ ₂ are each determined separately by a fitting process, but then the term B could not be neglected. There is no need to wait for a specific point in time for this fitting process, but the fit can be carried out continuously in a rolling time window of the measurement data. The method benefits from the fact that the sensors under consideration are closely coupled with regard to the ambient temperature due to their spatial proximity.

The ratio of τ ₁ and τ ₂ thus obtained is close to 1 if the switchgear 1 has no faults in the immediate vicinity of the two temperature sensors 18a...c, that is, in particular if the screw connections where the temperature sensors 18a...c are arranged do not cause any significant heat input. In this case, all heat sources of the switchgear 1 are approximately the same distance from the two temperature sensors 18a...c, since the temperature sensors 18a...c are arranged close to one another, for example on directly adjacent screw connections. As a result, current changes have approximately the same effect on both temperature sensors 18a...c and the resulting time constants are almost the same, i.e. have a ratio of approximately 1.

If, on the other hand, one of the screw connections is faulty, this causes heat input. Since this heat input now - in comparison to the distance between the temperature sensors 18a ... c - takes place very close to one of the two temperature sensors 18a ... c, the effect on the time constant of the two temperature sensors 18a ... c is different and the ratio of the Time constant now deviates significantly from 1. Tests have shown that the resulting ratios are around 0.6, for example.

The size of the ratio can therefore be used as a criterion as to whether an error is present. For this purpose, the distance of the ratio of 1 is compared with a predetermined threshold value of, for example, 0.2. If the distance from 1 is greater than the threshold, an alarm signal is triggered and/or a safety measure such as a shutdown is taken. In the present example, an alarm signal is triggered if the ratio is greater than 1.2 or less than 0.8. As an alternative to the distance, a factor can also be used by which the ratio deviates from 1 so that errors in both screw connections are treated mathematically in the same way. For example, if a factor of 0.8 is used, then an alarm signal is triggered if the ratio is less than 0.8 or greater than 1/0.8 = 1.25.

In addition to a comparison with an absolute threshold value, the profile of the determined ratio can also be viewed in order to determine an error. If the ratio increases or decreases significantly over time, for example by 10% within a predetermined period of time, an error can be assumed and an alarm signal can thus be triggered and/or a safety measure such as a shutdown can be implemented.

In a gas-insulated switchgear, the temperature sensors 18a...c can be arranged in or on a T-connector, among other things. 3 shows such a T-connector 40 in a sectional view with a plurality of possible positions 41...44 for the temperature sensor 18a...c. The positions differed by their distance from the screw connection and thus the temporal reaction to current changes. At a position that is very close to a possible fault, such as position 43, the thermal response can be described very well with a first-order thermal network, while at a position further away from the fault, such as position 42, a second-order thermal network better describes the temperature profile represents.

Reference List

1

air-insulated switchgear

2

equipment room

3

cable connection compartment

4

busbar room

5

low voltage room

10

switching device

11

bushings

12

upper outlet

13

lower outlet

14

busbar

15

Cable

16

connection conductor

17

evaluation unit

18a...c

temperature sensor

20

screw connection

21

thermal mass

22

thermal resistance

23

outside temperature

40

T connector

41...45

Positions for the temperature sensor

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• US 2017/0148300 A1 [0003]

Claims (10)

Method for operating a switchgear (1), in which - Signals from two temperature sensors (18a...c) arranged in the switchgear (1) are recorded, - by fitting a function that models a ratio of the temperature curves at the temperature sensors (18a...c), to which signals a ratio of two thermal time constants for temperature changes at the temperature sensors (18a...c) is determined, - an alarm signal is generated when the thermal time constant ratio is within an error range. procedure after claim 1 , where the error range includes all values for the ratio of the time constants that are further than a minimum distance of 1. procedure after claim 1 or 2 , in which the function describes the temperature curve assuming that the temperature sensors (18a...c) are connected to an ambient temperature (23) via a first-order thermal network with a thermal mass (21) and a thermal resistance (22). , where the ambient temperature (23) is not taken into account in the function. A method as claimed in any one of the preceding claims, in which a security measure is taken upon receipt of the alarm signal. procedure after claim 4 , in which the safety measure includes reducing a flowing current, switching off the switchgear (1) or initiating a maintenance measure. Switchgear (1) with at least two temperature sensors (18a...c) and an evaluation device (17), the evaluation device (17) being designed to carry out a method according to one of the preceding claims. switchgear (1) after claim 6 with a plurality of phases or switch panels, in particular three phases and a temperature sensor (18a...c) for each phase or each switch panel. switchgear (1) after claim 6 or 7 , in which the temperature sensors (18a...c) are designed to measure temperatures of screw connections. switchgear (1) after claim 8 , in which the temperature sensors (18a...c) are arranged on a busbar connection, a cable connection, an upper outlet (12), a lower outlet (13) or on a bushing (11). System with a switchgear (1) and a computer system that is designed apart from the switchgear (1), in particular as a cloud service, in which the computer system is designed to carry out a method according to one of the Claims 1 until 5 and the switchgear (1) is designed to transmit the temperature profile to the computer system.

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